Exhaust gas emitted from internal combustion engines such as gasoline engines and diesel engines of automobiles and motorbikes (alternatively referred to as “saddled vehicles”) contains harmful components such as hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOx), and the like. In particular, the purification of HC using a catalyst is significantly affected by the exhaust gas temperature, and, generally, a high temperature of 300° C. or more is required. Accordingly, when the exhaust gas temperature is low immediately after an internal combustion engine is started, it is difficult to purify HC using a catalyst. Moreover, immediately after an internal combustion engine is started, a large amount of HC tends to be emitted, and the proportion of HC in the entire emission amount is large when the exhaust gas temperature is low. Thus, the removal of HC from an internal combustion engine immediately after an internal combustion engine is started is a conventional problem.
Patent Literature 1 describes the use of a proton zeolite such as mordenite, as an HC adsorbent. Furthermore, Patent Literature 2 describes the use of Cu2+ exchange CHA zeolite, as a selective contact reduction catalyst for exhaust gas purification. Furthermore, Patent Literature 3 describes the use of phosphorus-supporting zeolite, as a catalytic cracking catalyst for hydrocarbons.